Piezoelectric element, piezoelectric element application device, and method of manufacturing piezoelectric element

ABSTRACT

A piezoelectric element includes a piezoelectric layer formed as a stacked structure of first, second, and third piezoelectric films. The first piezoelectric film is formed on a first electrode. The second piezoelectric film is formed on the first piezoelectric film. The third piezoelectric film is formed on the second piezoelectric film. Each of the first, second, and third piezoelectric films includes potassium, sodium, and niobium. A second electrode is formed on the piezoelectric layer. A concentration of sodium in the first piezoelectric film is greater than a concentration of sodium in the second piezoelectric film. The concentration of sodium in the second piezoelectric film is greater than a concentration of sodium in the third piezoelectric film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/378,474, filed Dec. 14, 2016, and which claims priority to JapanesePatent Application No. 2016-024082, filed Feb. 10, 2016, the disclosuresof which are hereby expressly incorporated by reference herein in theirentireties.

BACKGROUND 1. Technical Field

The present invention relates to a piezoelectric element, apiezoelectric element application device which is provided with apiezoelectric element, and a method of manufacturing a piezoelectricelement.

2. Related Art

In general, piezoelectric elements have a piezoelectric layer which haselectro-mechanical conversion characteristics, and two electrodes withthe piezoelectric layer interposed therebetween. In recent years,devices (piezoelectric element application devices) using suchpiezoelectric elements as a driving source have been actively developed.As a piezoelectric element application device, there are liquid ejectingheads which are represented by an ink jet recording head, MEMS elementswhich are represented by a piezoelectric MEMS element, ultrasonicmeasuring apparatuses which are represented by an ultrasonic sensor orthe like, as well as piezoelectric actuator apparatuses, and the like.

As a material (piezoelectric material) for the piezoelectric layer ofthe piezoelectric element, potassium sodium niobate ((K, Na) NbO₃,referred to below as “KNN”) has been proposed (for example, refer toJP-A-2009-038169). JP-A-2009-038169 describes that a KNN layer is formedby a sputtering method (gas phase method). Since a KNN sintered bodyproduced by a sintering method is the target in the sputtering method,it is difficult to homogenize the composition distribution (K:Na) at themicroscopic level. In addition, taking into account that non-homogeneityof the composition distribution at the microscopic level extends in thein-plane direction, it is considered that the KNN layer formed by thismethod has a homogeneous composition in the film thickness direction,but that it is difficult to make the composition in the in-planedirection homogeneous.

On the other hand, JP-A-2007-184513 describes forming the KNN layer byusing a wet method (liquid phase method). From the point of view ofstacking a KNN thin film with a homogeneous composition distribution(K:Na), it is considered that the KNN layer formed by this method has ahomogeneous composition in the in-plane direction. That is, in the wetmethod, when the KNN thin film is crystallized, the element distributionin the sol is homogeneous at the crystal cell (unit cell) level and itis possible to make the distribution homogeneous in the crystal growthdirection. Accordingly, the homogeneity of the composition in thein-plane direction of the KNN layer which is a stack of the KNN thinfilms is expected to be superior to that of a composition formed by thesputtering method.

However, in the wet method, since the KNN layer is formed by stackingthe KNN thin film, there is a composition distribution (K:Na) in thefilm thickness direction (it is difficult to make the compositionhomogeneous). Thus, there is a demand to realize homogeneity in thecomposition distribution in the in-plane direction and the filmthickness direction in KNN layers formed by a wet method.

Here, this problem is not only limited to piezoelectric elements used inpiezoelectric actuators mounted in a liquid ejecting head which isrepresented by an ink jet recording head, but this problem alsosimilarly affects piezoelectric elements used in other piezoelectricelement application devices.

SUMMARY

An advantage of some aspects of the present invention is to provide apiezoelectric element which has a KNN layer formed by a wet method whichis a piezoelectric layer with a homogeneous composition distribution inthe in-plane direction and the film thickness direction, a piezoelectricelement application device, and a method of manufacturing apiezoelectric element.

Here, as the result of extensive research, the present inventorsdiscovered that it is possible to form crystal grains having continuityby ensuring homogeneity of the whole KNN layer by making the shape of orchanges in the composition distribution (K:Na) in the film thicknessdirection homogeneous by controlling the thickness of a KNN thin filmwhich is a first layer, and making the crystal growth direction of eachof the KNN thin films in the KNN layer the same by maintaining thehomogeneity of the shape of the composition distribution.

According to an aspect of the invention, there is provided apiezoelectric element including a first electrode, a piezoelectric layerformed of a first piezoelectric film which is formed on the firstelectrode and which includes potassium, sodium, and niobium and aplurality of second piezoelectric films which are formed on the firstpiezoelectric film and which include potassium, sodium, and niobium, anda second electrode formed on the piezoelectric layer, in which thepiezoelectric layer is a stacked structure of a plurality ofpiezoelectric films, the first piezoelectric film has a thickness of 30nm to 70 nm, the concentration of sodium in each of the piezoelectricfilms is along a gradient in a film thickness direction with a firstelectrode side being high and a second electrode side being low.

In this aspect, it is possible to provide a piezoelectric element with ahomogeneous composition distribution in the in-plane direction and thefilm thickness direction in the piezoelectric layer. In addition,regarding the composition of the piezoelectric layer in the filmthickness direction, the concentration of the potassium and sodium ineach of the piezoelectric films is along a gradient; however, since theshape of and changes in the distribution of each of the piezoelectricfilms are substantially the same as each other, it is possible to obtaina piezoelectric element in which homogeneity in the piezoelectric layeras a whole is ensured.

Here, the piezoelectric element preferably includes the firstpiezoelectric film formed on the first electrode without a titanium filmbeing interposed therebetween. Accordingly, it is possible to eliminatefactors contributing to a decrease in the electric characteristics ofthe piezoelectric element.

In addition, according to another aspect of the present invention, thereis provided a piezoelectric element application device provided with thepiezoelectric element described above.

In this aspect, it is possible to provide a piezoelectric elementapplication device with stable piezoelectric and dielectriccharacteristics and robustness (mechanical characteristic) againstexternal stress.

Furthermore, according to still another aspect of the present invention,there is provided a method of manufacturing a piezoelectric element, themethod including forming a first electrode; forming a piezoelectriclayer by forming a first piezoelectric film with a thickness of 30 nm to70 nm including potassium, sodium, and niobium on the first electrodewith a wet method, and forming a plurality of second piezoelectric filmsincluding potassium, sodium, and niobium on the first piezoelectric filmwith a wet method; and forming a second electrode on the piezoelectriclayer, in which, when forming the piezoelectric layer, the concentrationof sodium in each of the piezoelectric films is along a gradient in afilm thickness direction, with a first electrode side being high and asecond electrode side being low.

In this aspect, it is possible to make the distribution of thecomposition in the piezoelectric layer homogeneous in the in-planedirection and the film thickness direction. In addition, in thecomposition of the piezoelectric layer in the film thickness direction,the concentration of potassium and sodium in each of the piezoelectricfilms is along a gradient; however, since the shape of and changes inthe distribution of each of the piezoelectric films are substantiallythe same as each other, it is possible to ensure the homogeneity of thepiezoelectric layer as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a perspective view which shows a schematic configuration of arecording apparatus.

FIG. 2 is an exploded perspective view of a recording head.

FIG. 3 is a plan view of the recording head.

FIG. 4 is a cross-sectional view of line IV-IV in FIG. 3.

FIG. 5 is a cross-sectional view which shows an example of a schematicconfiguration of a piezoelectric element.

FIG. 6 is a diagram which shows each starting point of thin filmcrystallization.

FIG. 7 is a cross-sectional view which shows an example of a thin filmcrystallization pattern.

FIG. 8 is a cross-sectional view which shows a method of manufacturing arecording head.

FIG. 9 is a cross-sectional view which shows a method of manufacturingthe recording head.

FIG. 10 is a cross-sectional view which shows a method of manufacturingthe recording head.

FIG. 11 is a cross-sectional view which shows a method of manufacturingthe recording head.

FIG. 12 is a cross-sectional view which shows a method of manufacturingthe recording head.

FIG. 13 is a cross-sectional view which shows a method of manufacturingthe recording head.

FIG. 14 is a cross-sectional view which shows a method of manufacturingthe recording head.

FIG. 15 is a diagram which shows a SIMS analysis profile of Example 1.

FIG. 16 is a diagram which shows a SIMS analysis profile of ComparativeExample 1.

FIG. 17 is a diagram which shows each X-ray diffraction pattern ofExample 1 and Comparative Example 1.

FIG. 18 is a diagram which shows each X-ray diffraction pattern ofExamples 1 and 2 and Comparative Examples 2 and 3.

FIG. 19 is a diagram which shows an X-ray diffraction pattern of asample a.

FIG. 20 is a diagram which shows an X-ray diffraction pattern of asample b.

FIG. 21 is a diagram which shows an X-ray diffraction pattern of asample c.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A description will be given below of embodiments of the presentinvention with reference to the drawings. However, the followingdescription illustrates one aspect of the present invention and can bechanged in an optional manner within the scope of the present invention.The same reference numerals are applied in each of the diagrams toillustrate the same members and explanation thereof is omitted asappropriate. In addition, in FIG. 2 to FIG. 5 and FIG. 8 to FIG. 14, X,Y, and Z represent three spatial axes which are perpendicular to eachother. In the present specification, a description will be given withthe directions along these axes set as the first direction X (Xdirection), the second direction Y (Y direction), and the thirddirection Z (Z direction), respectively, and the direction of the arrowsin each of the diagrams as the positive (+) direction and the directionopposite to the direction of the arrows as the negative (−) direction.The X direction and Y direction represent the in-plane direction of theplate, layer, and films and the Z direction represents the thicknessdirection or the stacking direction of the plate, layer, and films.

Embodiment 1

FIG. 1 is an ink jet recording apparatus which is an example of a liquidejecting apparatus provided with a recording head which is an example ofa piezoelectric element application device. As shown in the diagram, inthe ink jet recording apparatus (recording apparatus) I, cartridges 2Aand 2B, which form the ink supply means, are detachably attached as theink jet recording head unit (head unit) II which has a plurality of inkjet recording heads. The carriage 3 on which the head unit II is mountedis provided to be freely movable, in the axial direction, on a carriageshaft 5 attached to the apparatus main body 4 and, for example, ejectseach color ink composition and a black ink composition.

Here, by transmitting the driving force of the driving motor 6 to thecarriage 3 via a plurality of gears (not shown) and the timing belt 7,the carriage 3 on which the head unit II is mounted is moved along thecarriage shaft 5. On the other hand, a transport roller 8 is provided asa transport means in the apparatus main body 4, and a recording sheet Swhich is a recording medium such as paper is transported by thetransport roller 8. The transport means which transports the recordingsheet S is not limited to being the transport roller 8 and may be abelt, a drum, or the like.

According to a recording apparatus I, since an ink jet recording head(referred to below simply as a “recording head”) is provided, low costmanufacturing is possible. In addition, since improvements in thedisplacement characteristics of the piezoelectric element which formsthe piezoelectric actuator are expected, it is possible to improve theejection characteristics.

A description will be given of an example of a recording head 1 mountedon the recording apparatus I described above with reference to FIG. 2 toFIG. 4. FIG. 2 is an exploded perspective view of a recording head whichis an example of a liquid ejecting head. FIG. 3 is a plan view of thepiezoelectric element side of the substrate for forming a flow path andFIG. 4 is a cross-sectional view along line IV-IV in FIG. 3.

As shown in the diagram, a substrate 10 is, for example, formed of asilicon single crystal substrate, and pressure-generating chambers 12are formed therein. Then, the pressure-generating chambers 12partitioned by a plurality of partition walls 11 are aligned in the Xdirection in the same manner as a plurality of nozzle openings 21 whicheject the same color ink. Here, the material of the substrate 10 is notlimited to a silicon single crystal and may be, for example, SOI, aglass ceramic, stainless steel, or the like.

In the substrate 10, an ink supply path 13 and a communication path 14are formed on one end side of the pressure-generating chamber 12 in theY direction. The ink supply path 13 is formed such that the opening areais reduced by narrowing one side of the pressure-generating chamber 12in the X direction. In addition, the communication path 14 hassubstantially the same width as the pressure-generating chamber 12 inthe X direction. A communication portion 15 is formed on the outside (onthe +Y direction side) of the communication path 14. The communicationportion 15 forms a part of a manifold 100. The manifold 100 forms acommon ink chamber for each of the pressure-generating chambers 12. Inthis manner, a liquid flow path formed of the pressure-generatingchambers 12, the ink supply path 13, the communication path 14, and thecommunication portion 15 are formed on the substrate 10.

A nozzle plate 20 made of, for example, SUS is bonded on one surface(surface on the −Z direction side) of the substrate 10. Nozzle openings21 are provided aligned in the X direction on the nozzle plate 20. Thenozzle openings 21 communicate with each pressure-generating chamber 12.The nozzle plate 20 can be bonded to the substrate 10 by an adhesive, aheat welding film, or the like. Here, the material of the nozzle plate20 is not limited to SUS and may be, for example, a silicon singlecrystal, SOI, a glass ceramic, or the like.

On the other surface (the surface on the +Z direction side) of thesubstrate 10, a vibrating plate 50 is formed. The vibrating plate 50 is,for example, formed of an elastic film 51 formed on the substrate 10 andan insulating film 52 formed on the elastic film 51. The elastic film 51is, for example, formed of silicon dioxide (SiO₂) and the insulatingfilm 52 is, for example, formed of zirconium oxide (ZrO₂). The elasticfilm 51 need not be a member separate from the substrate 10. A part ofthe substrate 10 is processed to be thin and may be used as an elasticfilm. A detailed description will be given below of the insulating film52; however, when a piezoelectric layer including potassium (K) andsodium (Na) as constituent elements is formed, the insulating film 52has a function as a barrier which prevents the potassium and sodium fromreaching the substrate 10 by passing through first electrodes 60.

On the insulating film 52, a piezoelectric element 300 including firstelectrodes 60, the piezoelectric layer 70, and a second electrode 80 isformed with the adhesive layer 56 therebetween. Each material for thefirst electrodes 60 and second electrode 80 is preferably a noble metalsuch as platinum (Pt), iridium (Ir), or palladium (Pd). Each material ofthe first electrodes 60 and the second electrode 80 may be any materialwhich has conductivity. Each material of the first electrodes 60 andsecond electrode 80 may be the same or different.

The piezoelectric layer 70 is formed by a solution method (a wet method)and is a composite oxide (KNN-based composite oxide) with a perovskitestructure (ABO₃ type perovskite structure), which is illustrated by ABO₃in the General Formula and which includes potassium (K), sodium (Na),and niobium (Nb). That is, the piezoelectric layer 70 includes apiezoelectric material formed of a KNN-based composite oxide which isrepresented by Formula (1).

(K_(x), Na_(1-x)) NbO₃  (1)

(0.1≤x≤0.9)

As described above, the composite oxide represented by Formula (1) is aso-called KNN-based composite oxide. Since the KNN-based composite oxideis a lead-free piezoelectric material where the content of lead (Pb) orthe like is reduced, the biocompatibility is excellent and theenvironmental impact is also small. Moreover, among lead-freepiezoelectric materials, since the KNN-based composite oxide hasexcellent piezoelectric characteristics, the KNN-based composite oxidehas an advantage in that various types of characteristics are improved.In addition, since the KNN-based composite oxide has a comparativelyhigh Curie temperature compared with other lead-free piezoelectricmaterials (for example, BNT-BKT-BT; [(Bi, Na)TiO₃]-[(Bi, K)TiO₃]-[BaTiO₃]) and is not easily depolarized due to increases intemperature, use at high temperatures is possible.

In Formula (1), the content of K is preferably 30 mol % to 70 mol % withrespect to the total amount of the metal element forming the A site (inother words, the content of Na is 30 mol % to 70 mol % with respect tothe total amount of the metal elements forming the A site). That is, inFormula (1), it is preferable that 0.3≤x≤0.7. Accordingly, a compositeoxide having a composition with advantageous piezoelectriccharacteristics is formed. In addition, the content of K is morepreferably 35 mol % to 55 mol % with respect to the total amount of themetal element forming the A site (in other words, the content of Na is45 mol % to 65 mol % with respect to the total amount of the metalelements forming the A site). That is, in Formula (1), it is preferablethat 0.35≤x≤0.55. Accordingly, a composite oxide having a compositionwith more advantageous piezoelectric characteristics is formed.

The piezoelectric material which forms the piezoelectric layer 70 is notlimited to the composition represented by Formula (1) as long as thematerial is a KNN-based composite oxide. For example, other metalelements (additives) may be included in the A site and B site of thepotassium sodium niobate. Examples of such additives include manganese(Mn), lithium (Li), barium (Ba), calcium (Ca), strontium (Sr), zirconium(Zr), titanium (Ti), bismuth (Bi), tantalum (Ta), antimony (Sb), iron(Fe), cobalt (Co), silver (Ag), magnesium (Mg), zinc (Zn), copper (Cu),and the like.

One or more of these types of additives may be included. Typically, theadditive amount is 20% or less with respect to the total amount of theelements which are the main components, preferably 15% or less, and morepreferably 10% or less. Using the additives makes it easy to vary thecomposition and functions by improving the various characteristics;however, it is preferable that KNN be present in an amount of more than80% from the point of view of exhibiting characteristics derived fromKNN. Here, even in a case of a composite oxide including these otherelements, the composite oxide is preferably formed to have an ABO₃ typeperovskite structure.

The alkali metal of the A site may be excessively added with respect tothe stoichiometric composition. In addition, the alkali metal of the Asite may be insufficient with respect to the stoichiometric composition.Accordingly, the composite oxide of the present embodiment can also berepresented by Formula (2).

(K_(AX), Na_(Z(1-X))) NbO₃  (2)

(0.1≤x≤0.9, preferably 0.3≤x≤0.7, more preferably 0.35≤x≤0.55)

In Formula (2), A represents the amount of K and Na which may be addedexcessively or the amount of K and Na which may be insufficient. In acase where the amount of K and Na is excessive, 1.0<A. In a case wherethe amount of K and Na is insufficient, A<1.0. For example, if A=1.1,when the amount of K and Na in the stoichiometric composition is set to100 mol %, A=1.1 represents that K and Na of 110 mol % are included. IfA=0.9, when the amount of K and Na in the stoichiometric composition isset to 100 mol %, A=0.9 represents that K and Na of 90 mol % areincluded. Here, in a case where the alkali metal of the A site isneither excessive nor insufficient with respect to the stoichiometriccomposition, A=1. From the point of view of improving thecharacteristics, 0.85≤A≤1.15, preferably 0.90≤A≤1.10, and morepreferably 0.95≤A≤1.05.

The piezoelectric materials may also include materials having acomposition where one element is insufficient, materials having acomposition where one element is excessive, and materials having acomposition where one element is substituted with another element. Aslong as the basic characteristics of the piezoelectric layer are notchanged, a material that deviates from the stoichiometric composition bybeing insufficient or excessive, and a material where one element issubstituted with another element may also be included in thepiezoelectric material according to the present embodiment.

In addition, “the composite oxide with the ABO₃ type perovskitestructure including K, Na, and Nb” in the present specification is notlimited to only a composite oxide with an ABO₃ type perovskite structureincluding K, Na, and Nb. In other words, “the composite oxide with theABO₃ type perovskite structure including K, Na, and Nb” in the presentspecification includes piezoelectric materials represented by mixedcrystals including a composite oxide with a ABO₃ type perovskitestructure including K, Na, and Nb (for example, the KNN-based compositeoxide illustrated above) and another composite oxide having an ABO₃ typeperovskite structure.

The other composite oxide is not limited while within the scope of thepresent invention, but is preferably a lead-free piezoelectric material.In addition, the other composite oxide is more preferably a lead-freepiezoelectric material which does not contain bismuth (Bi). Accordingly,a piezoelectric element 300 having excellent biocompatibility and a lowenvironmental impact is formed.

The piezoelectric element 300 is formed via an adhesive layer 56 forimproving the adhesion of the first electrodes 60 and an underlayer (thesubstrate 10) described above. As the adhesive layer 56, it is possibleto use, for example, titanium oxide (TiO_(x)), titanium (Ti), siliconnitride (SiN), or the like. In addition, the adhesive layer 56 functionsas a stopper which prevents the potassium and sodium from reaching thesubstrate 10 by passing through the first electrodes 60 in the samemanner as the insulating film 52. Here, the adhesive layer 56 may beomitted.

In the present embodiment, the piezoelectric element 300 and thevibrating plate 50 which generates displacement due to the driving ofthe piezoelectric element 300 are collectively referred to as theactuator apparatus. In more detail, the vibrating plate 50 and the firstelectrodes 60 are displaced due to the displacement of the piezoelectriclayer 70 which has electro-mechanical conversion characteristics. Thatis, the vibrating plate 50 and the first electrodes 60 functionsubstantially as a vibrating plate without being limited thereto. Forexample, by omitting one or both of the elastic film 51 and theinsulating film 52, either the film and the first electrodes 60 or onlythe first electrodes 60 may be set to function as the vibrating plate.Alternatively, the piezoelectric element 300 itself may alsosubstantially function as the vibrating plate. In a case of providingthe first electrodes 60 directly on the substrate 10, it is preferableto protect the first electrodes 60 with a protective film or the likewith an insulating property such that ink does not contact the firstelectrodes 60.

In such a piezoelectric element 300, in general, one of the electrodesis a common electrode which is made to be in common and the otherelectrode is set to be an individual electrode (referred to below as an“individual electrode”) by patterning each of the pressure-generatingchambers 12. As will be described in detail below, in the presentembodiment, the first electrodes 60 are set as individual electrodes andthe second electrode 80 is set as a common electrode; however, there isno problem if the electrodes are reversed for the convenience of thedriving circuit 120 or the connection wiring 121. Here, in the presentembodiment, the common electrode is formed by continuously forming thesecond electrode 80 across the plurality of pressure-generating chambers12.

The first electrodes 60 are provided with a narrower width than thewidth of the pressure-generating chambers 12 in the X direction for eachregion opposing each of the pressure-generating chambers 12. Inaddition, the first electrodes 60 extend from one end side to above thecircumferential wall in the longitudinal direction (−Y direction) ofeach of the pressure-generating chambers 12. Then, lead electrodes 90formed of, for example, gold (Au) or the like are respectively connectedto the first electrodes 60 in regions outside the pressure-generatingchambers 12 and a voltage is selectively applied to each of thepiezoelectric elements 300 via the lead electrodes 90. That is, thefirst electrodes 60 form individual electrodes as described above. Onthe other hand, the ends of the first electrodes 60 on the other endside of the pressure-generating chambers 12 in the longitudinaldirection (+Y direction) are positioned inside a region opposing thepressure-generating chambers 12 when seen from the Z direction.

The piezoelectric layer 70 is provided between the first electrodes 60and the second electrode 80. The piezoelectric layer 70 is formed with awider width than the X direction width of the first electrodes 60 and,in addition, formed with a wider width than the Y direction width of thepressure-generating chambers 12. One end of the piezoelectric layer 70(end in the +Y direction) is formed further to the outside than one end(the end in the +Y direction) of the first electrodes 60 and the firstelectrodes 60 are covered by the piezoelectric layer 70. On the otherhand, the other end (end in the −Y direction) of the piezoelectric layer70 is further inside than the other end (end in the −Y direction) of thefirst electrodes 60 and the first electrodes 60 is covered by the leadelectrode 90.

When viewed from the Z direction, the second electrode 80 iscontinuously formed in a region which opposes the plurality ofpressure-generating chambers 12 and forms a common electrode asdescribed above. That is, the second electrode 80 is provided to coversubstantially the entirety of the upper surface of the piezoelectriclayer 70 of the region opposing the pressure-generating chambers 12 andboth end surfaces in the X direction. At the time of driving, a voltageis applied to the piezoelectric layer 70 of the region (driving portion)where the first electrodes and the second electrode 80 overlap. Sincethe upper surface and both end surfaces in the X direction of thepiezoelectric layer 70 are covered by the second electrode 80, thepermeation of moisture (humidity) in the atmosphere into thepiezoelectric layer 70 in accordance with the driving is prevented.Accordingly, it is possible to prevent damage to the piezoelectricelement 300 caused by moisture, and it is possible to remarkably improvethe durability of the piezoelectric element 300.

The protective substrate 30 is bonded by an adhesive 35 on the substrate10 on which the piezoelectric elements 300 are formed. The protectivesubstrate 30 has a manifold portion 32. At least a portion of themanifold 100 is formed of the manifold portion 32. In the presentembodiment, the manifold portion 32 extends through the protectivesubstrate 30 in the thickness direction (Z direction) and is formedacross the width direction (X direction) of the pressure-generatingchambers 12. Then, as described above, the manifold portion 32communicates with the communication portion 15 of the substrate 10.According to this configuration, the manifold 100 which forms a commonink chamber of each of the pressure-generating chambers 12 is formed.

In the protective substrate 30, a piezoelectric element holding portion31 is formed in a region including the piezoelectric element 300. Thepiezoelectric element holding portion 31 has a space large enough not tohinder the movement of the piezoelectric element 300. This space may besealed or may not be sealed. In addition, in the protective substrate30, a through hole 33 which passes through the protective substrate 30in the thickness direction (Z direction) is provided. In the throughhole 33, the ends of the lead electrodes 90 are exposed.

On the protective substrate 30, a driving circuit 120 which functions asa signal processing portion is fixed. The driving circuit 120 can use,for example, a circuit board or a semiconductor integrated circuit (IC).The driving circuit 120 and the lead electrode 90 are electricallyconnected via connection wiring 121 formed of conductive wiring such asbonding wiring inserted into the through hole 33. The driving circuit120 can be electrically connected to a printer controller 200 (refer toFIG. 1). This driving circuit 120 functions as a control means of theactuator apparatus (the piezoelectric element 300).

In addition, on the protective substrate 30, a compliance substrate 40formed of a sealing film 41 and a fixing plate 42 is bonded. The sealingfilm 41 is formed of a material with a low rigidity and the fixing plate42 can be formed of a hard material such as metal. When viewed from theZ direction, the region of the fixing plate 42 opposing the manifold 100forms an opening portion 43 which is completely removed in the thicknessdirection (the Z direction). One surface (the surface in the +Zdirection) of the manifold 100 is sealed only by the sealing film 41which has flexibility.

Here, examples of the material for the protective substrate 30 includeglass, ceramic material, metal, resin, and the like, and the protectivesubstrate 30 is more preferably formed by a material with substantiallythe same thermal expansion coefficient as the substrate 10. In thepresent embodiment, a silicon single crystal substrate which is the samematerial as the substrate 10 is used to form the protective substrate30.

Next, a detailed description will be given of the piezoelectric element300 with reference to FIG. 5. FIG. 5 is a cross-sectional view whichshows an example of a schematic configuration of the piezoelectricelement included in a recording head mounted on a recording apparatus.As shown in the diagram, the piezoelectric element 300 includes thefirst electrodes 60 with a thickness of approximately 50 nm, the secondelectrode 80 with a thickness of approximately 50 nm, and thepiezoelectric layer 70 provided between the first electrodes and thesecond electrode 80. At this time, the piezoelectric layer 70 is a stackof a plurality of piezoelectric films, and is formed of a firstpiezoelectric film 71 having a thickness of 30 nm to 70 nm and aplurality of second piezoelectric films 72 formed on the firstpiezoelectric film 71, and the concentration of the sodium in the firstpiezoelectric film 71 and the plurality of second piezoelectric films 72is along a gradient in the film thickness direction (Z direction), beinghigh on the first electrodes 60 side and low on the second electrode 80side.

The first piezoelectric film 71 and the second piezoelectric films 72each include potassium, sodium, and niobium. That is, the firstpiezoelectric film 71 and the second piezoelectric films 72 are formedof the KNN-based composite oxide described above, specifically, a KNNfilm formed of a KNN crystal which is highly oriented with apredetermined crystal plane due to the crystallization (crystallizationby a heat treatment to remove unnecessary substances such as solventsfrom a precursor solution of the KNN-based composite oxide).

In the present embodiment, in the piezoelectric layer 70, by definingthe thickness of the first piezoelectric film 71 within the rangedescribed above and further forming the plurality of secondpiezoelectric films 72 on the upper layer thereof, it is possible todefine the shape of and changes in the concentration distribution of thesodium in the first piezoelectric film 71 and the plurality of thesecond piezoelectric films 72. Due to this, in the piezoelectric layer70, it is possible to make the composition distribution homogeneous inthe in-plane direction (X direction) and the film thickness direction (Zdirection). At this time, the thickness of the plurality of secondpiezoelectric films 72 is preferably set to be respectively 50 nm to 100nm; however, the thickness is not particularly limited. In addition,FIG. 5 shows a configuration example of the piezoelectric element 300 inwhich two layers of the second piezoelectric films 72 are each formed onthe upper layer of the first piezoelectric film 71; however, theconfiguration is not limited thereto. In the piezoelectric element 300,since the piezoelectric layer 70 is a so-called thin film piezoelectricbody with a thickness of 50 nm to 2000 nm, after the thickness of thefirst piezoelectric film 71 is determined, the number of layers andthickness of the second piezoelectric films 72 are determined.

Here, the thickness of the first electrodes 60, the second electrode 80,and the piezoelectric layer 70 listed here are all examples and can bechanged within a range which does not depart from the gist of thepresent invention.

Next, according to the configuration described above, a detaileddescription will be given of the mechanism for homogenizing thecomposition distribution in the in-plane direction (X direction) and thefilm thickness direction (Z direction) in the piezoelectric layer 70.

FIG. 6 is a diagram which shows the respective starting points ofcrystallization in the thin film when forming the piezoelectric filmsand FIG. 7 is a cross-sectional view which shows an example of acrystallization pattern in the thin film when forming the firstpiezoelectric film. As shown in FIG. 6, it is considered that, ingeneral, there are three patterns in which the thin film crystallizesinto a piezoelectric body. That is, there are three starting points ofthe crystallization, which are (A) the interface with the lower layer(the first electrodes 60), (B) inside the thin film, and (C) the thinfilm surface. Since a condition for forming a starting point ofcrystallization is that the activation energy is low, whether thestarting point of the crystallization is the starting point (A), thestarting point (B), or the starting point (C) depends on the magnitudeof the activation energy at each location.

When the thickness of the first piezoelectric film 71 is less than 30nm, condensation occurs in the process of manufacturing thepiezoelectric layer, a place where the first piezoelectric film 71 ispresent and a place where the first piezoelectric film 71 is not presentare generated on the first electrodes 60, and the place where the firstpiezoelectric film 71 is not present leads to subsequent forming ofspaces in the piezoelectric layer 70, which causes an adverse effect onthe electric reliability, the mechanical reliability, and the continuousgrowth property in the orientation at the time of crystal growth.

In addition, when the thickness of the first piezoelectric film 71exceeds 70 nm, the starting point of the crystal growth moves to theinside of the thin film or to the thin film surface. In a case where thecrystal growth starting point is present in the first piezoelectric film71 (the starting point (B) in FIG. 6), since the starting point of thecrystal growth is equal in three dimensions, there is no factor whichdetermines the orientation, and, as a result, the orientation is random.In addition, in a case where the crystal growth starting point ispresent in the thin film surface (the starting point (C) in FIG. 6), asshown in FIG. 7, since the first electrodes 60 interface is the end ofthe crystal growth, a heterogeneous phase 73 is formed between the firstpiezoelectric film 71 and the first electrodes 60, and this is a factorbehind the electric resistance and the mechanical characteristics beingdecreased, or the crystal grains being prevented from growingcontinuously and the degree of orientation being decreased even whenoriented. In other words, when the thickness of the first piezoelectricfilm 71 is outside a suitable range, since continuous crystal growth isinhibited and continuous crystallization does not occur from on thefirst electrodes 60, the piezoelectric layer 70 is obtained in which thecomposition distribution is non-homogeneous, the orientation is random,and the orientation is insufficient even when oriented.

On the other hand, the thickness of the first piezoelectric film 71 isset to 30 nm to 70 nm, the starting point of the crystal growth moves tothe interfaces with the first electrodes 60 (starting point (A) in FIG.6). That is, when the KNN of the first piezoelectric film 71 iscrystallized, the crystallization starting point is not in the thin filmor on the thin film surface side, but is present on the first electrodes60 interface side, the gradient of the Na concentration of the firstpiezoelectric film 71 (KNN film) is low on the layer surface side andhigh at the first electrodes 60 interface side, and the gradient of theK concentration is naturally the reverse of the gradient of the Naconcentration. Due to the crystallization starting point being presenton the first electrodes 60 interface side, the crystal state of thefirst electrodes 60 oriented with the (111) plane is reflected, thecrystal plane is highly oriented with the (001) plane, and a KNN filmwhere the composition distribution is homogeneous in the in-planedirection and the film thickness direction is obtained. Forming theplurality of second piezoelectric films 72 (KNN film) on the layerobtains a KNN film where the crystal surface is highly oriented with the(001) plane is stacked by continuing from the orientation of the KNNfilm of the lower layer, and the piezoelectric layer (KNN layer) highlyoriented with the (001) plane. In addition, in the composition of thepiezoelectric layer 70 in the film thickness direction, theconcentration of K and Na in each of the piezoelectric films (KNN films)is along a gradient; however, since the shape of and the changes in thedistribution of each of the piezoelectric films are substantially thesame in all of the piezoelectric films, it is possible to ensure thehomogeneity of the piezoelectric layer 70 as a whole.

Then, using a wet method is extremely advantageous compared to using asputtering method for forming the piezoelectric layer 70 with ahomogeneous composition distribution with a large area (for example, asubstrate of inches or more) by enabling the realization of thepiezoelectric layer 70 which has homogeneity of the compositiondistribution in the film thickness direction.

Here, a noble metal (Pt, Ir, Pd, or the like) often used as an electrode(here as the first electrodes 60) has little surface free energy andstarting the crystallization of the KNN from the first electrodes 60surface is generally difficult. Here, a Ti film with a maximum thicknessof approximately 2 nm is film formed on the Pt or Ir surface. That is,since the surface free energy of the Ti is greater than that of the Ptor Ir, by forming a Ti film on the first electrodes 60 and forming thefirst piezoelectric film 71 (KNN film) on top thereof, the KNNcrystallization starting point is easily set on the first electrodes 60interface side and it is possible to obtain a first piezoelectric film71 highly oriented with the (001) plane. However, when the KNN thin filmis crystallized on the Ti film, the Ti atoms are diffused in the KNNthin film and defects which decrease the electrical resistance of thethin film are generated. Then, in the present embodiment, as describedabove, by setting the thickness of the first piezoelectric film 71 to 30nm to 70 nm, even when the Ti film is not formed on the first electrodes60, it is possible to obtain a first piezoelectric film 71 which ishighly oriented with the (001) plane by setting the Pt electrode (firstelectrodes 60) interface as the KNN crystal growth starting point. Here,this may not be the case in a case where measures are taken to preventdiffusion of the Ti atoms in the KNN thin film.

The Pt used as the first electrodes 60 is generally oriented with the(111) plane, it is possible to highly orient the first piezoelectricfilm 71 (KNN film) formed thereon with the (001) plane without formingthe Ti film which is an orientation control layer. In the presentinvention, on the Pt first electrodes 60 oriented with the (111) plane,by setting the thickness of the first piezoelectric film 71 of the KNNfilm to 30 nm to 70 nm, it is possible orient the first piezoelectricfilm 71 with the (001) plane. Although the reason therefor is not clear,the following mechanisms can be considered.

That is, a model may be considered in which, when the KNN iscrystallized on the Pt oriented with the (111) plane, the orientationstate of the Pt is dragged and pyrochlore (an intermediate product) witha lower crystallization temperature than the KNN is oriented with the(111) plane on the Pt and, when the KNN is crystallized thereon, a KNNcore where an oxygen octahedron is crystallized is formed in thepyrochlore and the pyrochlore is lost as the crystallization of the KNNprogresses. In other words, it is considered that, since the pyrochloreformed on the Pt oriented with the (111) plane is oriented with the(111) plane, the oxygen octahedron in the natural pyrochlore is also inan oriented state and is re-crystallized as KNN by moving to a positionwhere the K and Na in the pyrochlore adopt a perovskite structure as thestarting point of the oriented oxygen octahedron, thus the KNN isoriented with the (001) plane and the pyrochlore is lost at the stagewhere the crystallization of the KNN ends.

Here, the piezoelectric layer 70 formed of the piezoelectric film (KNNfilm) highly oriented with the (001) plane refers to a layer where theKNN crystal is preferentially oriented with the (001) plane in thepresent embodiment. For example, the piezoelectric layer 70 formed of aKNN-based composite oxide is easily naturally oriented with the (001)plane. In addition, the piezoelectric layer 70 may be preferentiallyoriented with the (110) plane or the (111) plane using a predeterminedorientation control layer provided as necessary. The piezoelectric layer70 preferentially oriented with a predetermined crystal plane easilyimproves various characteristics in comparison with a randomly orientedpiezoelectric layer. Here, in the present specification, preferentialorientation refers to 50% or more, preferably 80% or more, of thecrystal being oriented with a predetermined crystal plane. For example,“preferentially oriented with the (001) plane” includes a case where allof the crystal of the piezoelectric layer 70 is oriented with the (001)plane and a case where half or more of the crystal (50% or more,preferably 80% or more) is oriented with the (001) plane.

In addition, since the piezoelectric layer 70 is polycrystalline, thestress in the plane is dispersed and homogeneous, thus stress fracturesdo not easily occur in the piezoelectric element 300 and the reliabilityis high.

The crystalline state of the piezoelectric layer 70 mainly changesaccording to the composition ratio of elements forming the piezoelectricbody and the conditions (for example, the firing temperature, thetemperature increase rate of the firing, and the like) when forming thepiezoelectric layer 70. Adjusting these conditions as appropriate makesit possible to control the crystal system of the piezoelectric layer 70such that a peak derived from a predetermined crystal plane is observed.

Next, with reference to FIG. 8 to FIG. 14, a description will be givenof an example of the method of manufacturing the piezoelectric element300 in conjunction with a method of manufacturing a recording head 1mounted on the recording apparatus I. FIG. 8 to FIG. 14 arecross-sectional views which show a method of manufacturing a recordinghead which is an example of a liquid ejecting head.

First, as shown in FIG. 8, by preparing the wafer 110 which is a siliconsubstrate and subjecting the wafer 110 to thermal oxidation, an elasticfilm 51 formed of silicon dioxide is formed on the surface thereof.Next, a zirconium film is formed by a sputtering method on the elasticfilm 51 and the insulating film 52 is formed by subjecting the zirconiumfilm to thermal oxidation. In this manner, a vibrating plate 50 formedof the elastic film 51 and the insulating film 52. Then, the adhesivelayer 56 formed of titanium oxide is formed on the insulating film 52 bya sputtering method, thermal oxidation of the titanium film, or thelike, and the first electrodes 60 are formed on the adhesive layer 56 bya sputtering method, an evaporation method, or the like.

Next, as shown in FIG. 9, the resist with a predetermined shape which isnot shown is formed as a mask on the first electrodes 60, and the firstelectrodes 60 and the adhesive layer 56 are patterned at the same time.Next, as shown in FIG. 10, the first piezoelectric film 71 is formed soas to overlap with the first electrodes 60 and the vibrating plate 50and a plurality of layers of the second piezoelectric films 72 areformed on the upper layer thereof. The piezoelectric layer 70 is formedby the plurality of layers of piezoelectric films.

In addition, it is possible to form the piezoelectric layer 70 by, forexample, a solution method such as a MOD method or a sol-gel method(chemical solution method). In this manner, using the solution method(wet method), by forming the piezoelectric layer 70, it is possible toincrease the productivity of the piezoelectric layer 70. Thepiezoelectric layer 70 formed by a wet method has the firstpiezoelectric film 71 which is a KNN film formed by a series of stepsfrom a step of coating a precursor solution to be described below(coating step) up to a step of firing a precursor film (firing step),and a plurality of the second piezoelectric films 72 which are KNN filmsformed by a series of steps in the same manner on the upper layerthereof. That is, the piezoelectric layer 70 is formed by repeating theseries of steps a plurality of times from the coating step up to thefiring step. Here, in the series of steps from the coating step up tothe firing step in the forming of the first piezoelectric film 71 andthe second piezoelectric films 72, after repeating from the coating stepto a degreasing step (to be described below) a plurality of times, a KNNfilm may be formed by carrying out a firing step. In the Examples whichwill be described below, a manufacturing example is given where thefirst piezoelectric film 71 and each of the second piezoelectric films72 are formed by performing the series of steps from the coating step upto the firing step one time; however, as long as it is possible to setthe thickness of the first piezoelectric film 71 to 30 nm to 70 nm andset each of the second piezoelectric films 72 to, for example, 50 nm to100 nm, the number of repetitions from the coating step up to thedegreasing step is not limited.

That is, in the present embodiment, the “forming the first piezoelectricfilm 71 with a thickness of 30 nm to 70 nm” has the meaning of forming athin film (KNN film) formed of a KNN crystal with a thickness of 30 nmto 70 nm. That is, the number of repetitions from the coating step tothe degreasing step is not limited; however, ultimately, the thicknessof the KNN film, that is, the first piezoelectric film 71 obtainedthrough the firing step, may be in the range described above. In thesame manner, “forming a plurality of the second piezoelectric films 72”has the meaning of forming two layers or more of KNN films. That is, thenumber of repetitions from the coating step up to the degreasing step isnot limited; however, ultimately, it is sufficient if two layers or moreof the second piezoelectric films 72 which are KNN films formed throughthe firing step are formed. That is, at the time of carrying out thefiring step, the thickness of the first piezoelectric film 71 and thesecond piezoelectric films 72 is determined. In the present embodiment,the piezoelectric layer 70 is formed by combining the firstpiezoelectric film 71 and the plurality of second piezoelectric films 72formed in this manner.

A layer or film formed by a wet method has an interface. Evidence of thecoating or firing remains on the layer or film formed by the wet methodand this evidence is an “interface” which can be confirmed by observingthe cross-section thereof or analyzing the concentration distribution ofelements in the layer (or in the film). Strictly speaking, the“interface” has the meaning of the boundary between the layers orbetween the films; however, here, the meaning is the vicinity of theboundary of the layers or films. In a case of observing thecross-section of the layer or film formed by a wet method, the interfaceis confirmed as a portion where the color is darker than the others or aportion where the color is lighter than the others in the vicinity ofthe boundary of the adjacent layer or film. In addition, in a case ofanalyzing the concentration distribution of the elements, the interfaceis confirmed as a portion where the concentration of the element ishigher than in other portions or a portion where the concentration ofthe element is lower than in other portions in the vicinity of theboundary of the adjacent layer or film. Since the piezoelectric layer 70is formed by repeating from the coating step up to the firing step aplurality of times (formed by a plurality of piezoelectric films), thereare a plurality of interfaces corresponding to each of the piezoelectricfilms. That is, the piezoelectric layer 70 has an interface for eachcoating step and has a different interface for each firing step.However, in the interfaces formed for each coating step, the shape ofand changes in the concentration distribution of the sodium or potassiumare hardly influenced, and the concentration of each of the elementschanges greatly for each firing step. That is, as described above, thesodium concentration in the first piezoelectric film 71 and theplurality of second piezoelectric films 72 is along a gradient in thefilm thickness direction (Z direction), being high on the firstelectrodes 60 side and low on the second electrode 80 side, and theconcentration of the potassium is the reverse of that of the sodium.

The specific procedure in a case of forming the piezoelectric layer 70with a solution method (wet method) is, for example, as follows. First,a precursor solution which includes a predetermined metal complex isadjusted. The precursor solution is a solution in which a metal complexwhich is able to form a composite oxide including K, Na, and Nb byfiring is dissolved or dispersed in an organic solvent. At this time,metal complexes which include additives such as Mn may be further mixedtherein.

Examples of metal complexes which include K include potassium 2-ethylhexane acid, potassium acetate, and the like. Examples of metalcomplexes which include Na include sodium 2-ethyl hexane acid, sodiumacetate, and the like. Examples of metal complexes which include Nbinclude niobium 2-ethyl hexane acid, pentaethoxyniobium, and the like.In a case of adding Mn as an additive, examples of metal complexes whichinclude Mn include manganese 2-ethyl hexane acid, and the like. At thistime, two or more metal complexes may be used in combination. Forexample, potassium 2-ethylhexyl hexane acid and potassium acetate may beused in combination as a metal complex which includes K. Examples of thesolvent include 2-n-butoxyethanol, n-octane, mixed solvents thereof, orthe like. The precursor solution may include an additive whichstabilizes the dispersion of the metal complex including K, Na, and Nb.Examples of such additives include 2-ethylhexanoic acid.

Then, the precursor solution is coated on the wafer 110 formed of thevibrating plate 50 and the first electrodes 60 to form a precursor film(coating step). Next, the precursor film is heated to a predeterminedtemperature, for example, approximately 130° C. to 250° C. and dried fora set time (drying step). Next, the dried precursor film is degreased bybeing heated to a predetermined temperature, for example, approximately300° C. to 450° C., and held at this temperature for a set time(degreasing step). Finally, when the KNN is crystallized by heating thedegreased precursor film to a higher temperature, for example, 650° C.to 800° C. and holding the film at this temperature for a set time, thefirst piezoelectric film 71 is completed (firing step). In the samemanner as the first piezoelectric film 71, by going through the seriesof steps from the coating step up to the firing step, the KNN iscrystallized to form the second piezoelectric films 72, the secondpiezoelectric films 72 are formed thereon in sequence in the samemanner, and a plurality of layers of the second piezoelectric films 72are completed. Due to this, the piezoelectric layer 70 formed of thefirst piezoelectric film 71 and a plurality of layers of the secondpiezoelectric films 72 is formed.

Examples of the heating apparatus used in the drying step, thedegreasing step, and the firing step include a Rapid Thermal Annealing(RTA) apparatus which heats by irradiation with an infrared lamp, a hotplate, or the like.

In addition, before and after forming the second electrode 80 on thepiezoelectric layer 70, a reheating process (post-annealing) may beperformed in a temperature range of approximately 600° C. to 800° C.according to necessity. In this manner, by performing thepost-annealing, it is possible to form a favorable interface between thepiezoelectric layer 70 and the first electrodes 60 or the secondelectrode 80, and it is possible to improve the crystallinity of thepiezoelectric layer 70.

In the present embodiment, an alkali metal (K or Na) is included in thepiezoelectric material. The alkali metal is easily diffused in the firstelectrodes 60 in the firing step described above. If the alkali metalreaches the wafer 110 by passing through the first electrodes 60, thealkali metal will react with the wafer 110. However, in the presentembodiment, the insulating film 52 formed of the zirconium oxidedescribed above functions as a stopper for K or Na. Accordingly, it ispossible to suppress the alkali metal from reaching the wafer 110 whichis a silicon substrate.

After that, the piezoelectric layer 70 formed of the first piezoelectricfilm 71 and the plurality of layers of the second piezoelectric films 72are patterned and shaped as shown in FIG. 11. It is possible for thepatterning to be performed by dry etching such as reactive ion etchingor ion milling, or wet etching using an etchant. After that, the secondelectrode 80 is formed on the piezoelectric layer 70. It is possible toform the second electrode 80 using the same method as the firstelectrodes 60. Through the above steps, the piezoelectric element 300provided with the first electrodes 60, the piezoelectric layer 70, andthe second electrode 80 is completed. In other words, the portion wherethe first electrodes 60, the piezoelectric layer 70, and the secondelectrode 80 overlap forms the piezoelectric element 300.

Next, as shown in FIG. 12, the protective substrate wafer 130 is bondedwith the surface of the wafer 110 on the piezoelectric element 300 sidevia an adhesive 35 (refer to FIG. 4). After that, the surface of theprotective substrate wafer 130 is thinned by abrasion. In addition, themanifold portion 32 and the through hole 33 (refer to FIG. 4) are formedin the protective substrate wafer 130. Next, as shown in FIG. 13, a maskfilm 53 is formed on the surface of the wafer 110 on the opposite sideto the piezoelectric element 300 and patterned into a predeterminedshape. Then, as shown in FIG. 14, anisotropic etching (wet etching)using an alkali solution such as KOH is carried out on the wafer 110 viathe mask film 53. Due to this, in addition to the pressure-generatingchambers 12 corresponding to the individual piezoelectric elements 300,an ink supply path 13, the communication path 14, and the communicationportion 15 (refer to FIG. 4) are formed.

Next, unnecessary portions of the outer peripheral edge of the wafer 110and the protective substrate wafer 130 are cut and removed by dicing orthe like. Furthermore, the nozzle plate 20 (refer to FIG. 4) is bondedwith the surface of the wafer 110 on the opposite side to thepiezoelectric element 300. In addition, the compliance substrate 40(refer to FIG. 4) is bonded with the protective substrate wafer 130.Through the steps up to this point, the assembly of the chips of therecording head 1 is completed. The recording head 1 (refer to FIG. 2,and the like) is obtained by dividing the assembly into individualchips.

In the recording head 1 having the configuration as described above,after taking in ink from an external ink supply means (for example, thecartridges 2A and 2B in FIG. 1) and filling the inner portion from themanifold 100 up to the nozzle opening 21 with ink, by applying a voltageto each of the piezoelectric element 300 corresponding topressure-generating chamber 12 in accordance with the recording signalfrom the driving IC (for example, driving circuit 120) and flexing andchanging the shape of the piezoelectric element 300, the pressure ineach of the pressure-generating chambers 12 is increased and inkdroplets are ejected from the nozzle openings 21.

That is, the piezoelectric element 300 described above is apiezoelectric element 300 with a flexural vibration mode. When thepiezoelectric element 300 with a flexural vibration mode is used, by thepiezoelectric layer shrinking in an orthogonal direction (piezoelectricelement holding portion 31 direction) to the application direction ofthe voltage along with the application of the voltage, the piezoelectricelement 300 and the vibrating plate 50 flex to the pressure-generatingchamber 12 side, due to which the pressure-generating chamber 12 iscontracted. On the other hand, due to the piezoelectric layer 70extending in the piezoelectric element holding portion 31 direction byreducing the application voltage, the piezoelectric element 300 and thevibrating plate 50 flex to the opposite side of the pressure-generatingchambers 12, due to which the pressure-generating chamber 12 isexpanded. In the recording head 1, since the volume of thepressure-generating chambers 12 changes in correspondence with thecharging and discharging of the piezoelectric element 300, it ispossible to eject liquid droplets from the nozzle openings 21 by usingthe pressure changes in the pressure-generating chambers 12.

EXAMPLES

A description will be given below of Examples of the present invention.Here, the present invention is not limited to the following Examples.

Example 1

By thermal oxidation of the surface of the silicon substrate which isthe substrate 10, the elastic film 51 formed of silicon dioxide wasformed on the silicon substrate. Next, by forming a zirconium film by asputtering method on the elastic film 51 and carrying out thermaloxidation on the zirconium film, the insulating film 52 formed ofzirconium oxide was formed. Next, by forming a titanium film by asputtering method on the insulating film 52 and carrying out thermaloxidation on the titanium film, an adhesive layer 56 formed of titaniumoxide was formed. Then, after forming a platinum film by a sputteringmethod on the adhesive layer 56, by pattering into a predeterminedshape, the first electrodes 60 with a thickness of 50 nm were formed.

Next, the piezoelectric layer 70 was formed by the following procedure.First, a 2-n-butoxyethanol solution of potassium acetate, an n-octanesolution of sodium acetate, and a 2-n-ethylhexanoic acid solution ofpentaethoxyniobium were mixed and precursor solution (K/Na=1/1) with asol concentration (metal element concentration) of 0.6 M/L was prepared.

Next, the prepared precursor solution was coated on the siliconsubstrate described above where the first electrodes 60 were formed, bya spin coating method at 1500 rpm to 3000 rpm (coating step). Next, thesilicon substrate was placed on a hot plate and dried for five minutesat 180° C. (drying step). Next, degreasing was performed for 10 minutesat 350° C. with respect to the silicon substrate on the hot plate(degreasing step). Next, firing was performed for five minutes at 750°C. using an RTA apparatus (firing step). Then, the first piezoelectricfilm 71 (KNN film) with a thickness of 70 nm was formed.

Next, by repeating from the coating step to the firing step a furthersix times, the second piezoelectric films 72 of the second to seventhlayers with a thickness of 80 nm were each formed, and the piezoelectriclayer 70 (KNN layer) with a thickness of 550 nm formed of seven layersof piezoelectric films was formed.

Example 2

The piezoelectric layer 70 of Example 2 was formed in the same manner asExample 1 except that the first piezoelectric film 71 with a thicknessof 35 nm was formed, and the piezoelectric layer 70 with a thickness of515 nm formed of seven layers of piezoelectric films was formed.

Comparative Example 1

The piezoelectric layer 70 of Comparative Example 1 was formed in thesame manner as Example 1 except that the first piezoelectric film 71with a thickness of 80 nm was formed, and the piezoelectric layer 70with a thickness of 560 nm formed of seven layers of piezoelectric filmswas formed.

Comparative Example 2

The piezoelectric layer 70 of Comparative Example 2 was formed in thesame manner as Example 1 except that the first piezoelectric film 71with a thickness of 112 nm was formed, and the piezoelectric layer 70with a thickness of 592 nm formed of seven layers of piezoelectric filmswas formed.

Comparative Example 3

The piezoelectric layer 70 of Comparative Example 3 was formed in thesame manner as Example 1 except that the first piezoelectric film 71with a thickness of 27 nm was formed, and the piezoelectric layer 70with a thickness of 507 nm formed of seven layers of piezoelectric filmswas formed.

SIMS Analysis

For Example 1 and Comparative Example 1, the depth directionconcentration profiles of each of sodium (Na) and potassium (K) from thesurface side of each piezoelectric layer 70 to the first electrodes 60were measured using secondary ion mass spectrometry (SIMS). FIG. 15shows the SIMS analysis profile of the piezoelectric layer 70 of Example1 and FIG. 16 shows the SIMS analysis profile of the piezoelectric layer70 of Comparative Example 1.

As shown in FIG. 15, the Na concentration was increased on the firstpiezoelectric film 71 side (substrate side) of the lower layer in thepiezoelectric layer 70 of Example 1. On the other hand, the Kconcentration was lowered at the first piezoelectric film 71 side of thelower layer and increased at the surface side of the piezoelectric filmsof each layer in the piezoelectric layer 70. Here, in FIG. 15, the leftside (side of the x axis where the etching time is 0) of the diagram isthe surface of the piezoelectric layer 70 and the interior of thepiezoelectric layer 70 is illustrated toward the right side (side of thex axis where the etching time is 1000) of the diagram. In addition, thegradient degree of the Na concentration and the gradient degree of the Kconcentration in each of the layers of the piezoelectric films werehomogeneous without difference between each of the layers of thepiezoelectric films.

As shown in FIG. 16, in the piezoelectric layer 70 of ComparativeExample 1, the Na concentration was low on the first piezoelectric film71 side (substrate side) of the lower layer and the K concentration washigh on the first piezoelectric film 71 side of the lower layer and theconcentrations of Na and K had the opposite results to the profile ofExample 1. The piezoelectric layer 70 of Comparative Example 1 had loweradhesion between the first piezoelectric film 71 and the firstelectrodes 60. In addition, as shown in FIG. 16, the gradient of the Kconcentration was not homogeneous and the piezoelectric and dielectriccharacteristics depending on the composition (K:Na ratio) were notstable. Furthermore, the columnar shape of the crystal grains was lostand the toughness (mechanical characteristic) with respect to externalstresses was decreased.

XRD Measurement

For each of Example 1, Example 2, and Comparative Examples 1 to 3,measurement of the X-ray diffraction pattern was performed using anX-ray diffraction (XRD) method. FIG. 17 shows the X-ray diffractionpatterns of Example 1 and Comparative Example 1 and FIG. 18 shows theX-ray diffraction patterns of Examples 1 and 2 and Comparative Examples2 and 3.

In general, in the X-ray diffraction pattern of the KNN layer, a peakwhere 2θ is derived in the (001) plane in the vicinity of 22.5° and apeak where 2θ is derived in the (110) plane in the vicinity of 32.0° areobserved. As shown in FIGS. 17 and 18, in the piezoelectric layer 70(KNN layer) of Examples 1 and 2, since a large peak where 2θ is in thevicinity of 22.5° is observed and a peak where 2θ is in the vicinity of32.0° is not observed, the piezoelectric layers 70 were clearly orientedwith the (001) plane.

On the other hand, as shown in FIG. 17 and FIG. 18, in the piezoelectriclayers 70 of Comparative Examples 1 and 2, peaks where 2θ is in thevicinity of 22.5° and in the vicinity of 32.0° are observed; however,since the peak where 2θ is in the vicinity of 22.5° is smaller than thepeaks of Examples 1 and 2, although oriented with the (001) plane, itwas clear that the orientation was less than that of Examples 1 and 2.In addition, in the piezoelectric layer 70 of Comparative Example 3, alarge peak where 2θ is in the vicinity of 22.5° is observed and a peakwhere 2θ is in the vicinity of 32.0° is hardly observed; however, sincethe peak where 2θ is in the vicinity of 22.5° is smaller than the peaksof Examples 1 and 2, although oriented with the (001) plane, it wasclear that the orientation was less than that of Examples 1 and 2.

Here, in FIGS. 17 and 18, the peak where 2θ is observed in the vicinityof 40° is a peak derived from the platinum forming the first electrodes60.

In Example 1, according to the SIMS analysis, it is clear that a largeamount of Na was present on the first electrodes 60 side of thepiezoelectric layer 70. In other words, as will be described in detailbelow, in consideration of NaNbO₃ being more easily crystallized thanKNbO₃, it is considered that, since the KNN crystallizes from the firstelectrodes 60 side, the crystal state of the KNN crystal on the firstelectrodes 60 side is easily continued, and the KNN is crystallized bycontinuing with the information of the orientation from the firstelectrodes 60. As a result, since the KNN is continuously oriented withthe (001) plane from the first electrodes 60, it is considered to show astrong orientation with the (001) plane in the XRD measurement results.

On the other hand, in Comparative Example 1, according to the SIMSanalysis, it is clear that a large amount of Na is not present on thefirst electrodes 60 side in the first piezoelectric film 71 on the firstelectrodes 60. That is, since the KNN is not crystallized from the firstelectrodes 60 side and the orientation of the KNN crystal on the firstelectrodes 60 side is not easily continued, it is considered that theorientation with the (001) plane in the KNN is weak in the firstpiezoelectric film 71 on the first electrodes 60. Then, in the secondpiezoelectric film 72 of the second layer formed on the firstpiezoelectric film 71 in this manner, since the orientation with the(001) plane is already weak even when the amount of Na on the firstelectrodes 60 side is great, it is considered that the piezoelectricfilm 74 is subsequently stacked as it is with the weak orientation withthe (001) plane. That is, when the first piezoelectric film of KNN isnot oriented with the (001) plane, it is inferred that the piezoelectricfilm of the layer thereon is also not oriented with the (001) plane.

Factor Determining Na Concentration Gradient and K ConcentrationGradient

The measurement of the X-ray diffraction patterns was performed for eachof a sample a where a film formed of a single composition of NaNbO₃ wasformed by firing at 550° C., a sample b where a film formed of a singlecomposition of KNbO₃ was formed by firing at 550° C., and a sample cwhere a film formed of a single composition of KNbO₃ was formed byfiring at 650° C. The X-ray diffraction pattern of sample a is shown inFIG. 19, the X-ray diffraction pattern of sample b is shown in FIG. 20,and the X-ray diffraction pattern of sample c is shown in FIG. 21.

As shown in FIG. 19, since the peak derived from <100> of NaNbO₃ where2θ is in the vicinity of 22° was observed, it is understood that NaNbO₃crystallizes when fired at 550° C. On the other hand, as shown in FIG.20, for KNbO₃, a peak derived from ZrO2 where 2θ is in the vicinity of28° is observed at a firing temperature of 550° C., and, as shown inFIG. 21, since the peak derived from <100> of KaNbO₃ is not observedwhen the firing temperature does not reach 650° C., it is understoodthat KNbO₃ crystallizes easily at 650° C. without crystallizing when thefiring temperature is 550° C. From this result, in a case of firing andproducing the KNN, it is understood that the Na concentration is highand the K concentration is low in the place which is the starting pointwhere the crystallization starts.

That is, in Example 1, that the gradient of the Na concentration of thefirst piezoelectric film 71 is low at the layer surface side and high atthe first electrodes 60 interface side has the meaning that thecrystallization starting point is not at the thin film surface side, butat the first electrodes 60 interface side when the KNN of the firstpiezoelectric film 71 is crystallized. On the other hand, in ComparativeExample 1, that the gradient of the Na concentration of the firstpiezoelectric film 71 is the opposite of Example 1 has the meaning thatthe crystallization starting point is not on the first electrodes 60interface side, but on the thin film surface side when crystallizing theKNN of the first piezoelectric film 71.

That is, the factor determining the Na concentration gradient and the Kconcentration gradient is not the firing temperature, but the thicknessof the first piezoelectric film 71. By setting the thickness of thefirst piezoelectric film 71 to 30 nm to 70 nm, the gradient of the Naconcentration of the first piezoelectric film 71 is low at the layersurface side and high at the first electrodes 60 interface side andnaturally, the gradient of the K concentration is the reverse of thegradient of the Na concentration. Due to this, it is inferred that it ispossible to obtain the piezoelectric layer 70 where the compositiondistribution is homogeneous in the in-plane direction and the filmthickness direction.

Other Embodiments

Description was given above of embodiments of a piezoelectric material,a piezoelectric element, a liquid ejecting head, and a liquid ejectingapparatus on which the piezoelectric element is mounted of the presentinvention; however, the basic configuration of the present invention isnot limited to the above description.

In the first embodiment described above, description was given of an inkjet recording head as a liquid ejecting head; however, the presentinvention is broadly applicable to liquid ejecting heads in general andapplication is naturally possible to a liquid ejecting head which ejectsa liquid other than ink. Examples of other liquid ejecting heads includevarious recording heads used in image recording apparatuses such asprinters, color material ejecting heads used in the manufacturing ofcolor filters such as liquid crystal displays, organic EL displays,electrode material ejecting heads used when forming electrodes such asfield emission displays (FED), bio material ejecting heads used inbiochip manufacturing, and the like.

In addition, the present invention is not limited to a piezoelectricelement mounted on a liquid ejecting head, and application is alsopossible to a piezoelectric element mounted on another piezoelectricelement application device. Examples of piezoelectric elementapplication devices include ultrasonic devices, motors, pressuresensors, pyroelectric element, ferroelectric elements, and the like. Inaddition, a complete body utilizing these piezoelectric elementapplication devices, for example, an apparatus ejecting liquid or thelike using the head ejecting liquid or the like described above, anultrasound sensor using the ultrasonic device described above, a robotwhere the motor described above is used as the driving source, an IRsensor using the pyroelectric element described above, a ferroelectricmemory using a ferroelectric element, and the like are also included inthe piezoelectric element application devices.

The constituent elements shown in the drawings, that is, thethicknesses, widths, relative positional relationships and the like ofthe layers or the like may be enlarged in order to illustrate thepresent invention. In addition, the term “on” in the presentspecification is not limited to meaning that the positional relationshipof the constituent elements is “directly on”. For example, theexpressions “first electrode on the substrate” or “piezoelectric layeron the first electrode” does not exclude including other constituentelements between the substrate and the first electrode or between thefirst electrode and the piezoelectric layer.

What is claimed is:
 1. A piezoelectric element comprising: a firstelectrode; a piezoelectric layer formed of a first piezoelectric filmformed on the first electrode; a second piezoelectric film formed on thefirst piezoelectric film, and a third piezoelectric film formed on thesecond piezoelectric film, each of the first, second, and thirdpiezoelectric films including potassium, sodium, and niobium; and asecond electrode formed on the piezoelectric layer, wherein thepiezoelectric layer is a stacked structure of the first, second, andthird piezoelectric films, and a concentration of sodium in the firstpiezoelectric film is greater than a concentration of sodium in thesecond piezoelectric film, and the concentration of sodium in the secondpiezoelectric film is greater than a concentration of sodium in thethird piezoelectric film.
 2. The piezoelectric element according toclaim 1, wherein the first piezoelectric film formed on the firstelectrode is provided without a titanium film interposed therebetween.3. A piezoelectric element application device comprising: thepiezoelectric element according to claim
 1. 4. A piezoelectric elementapplication device comprising: the piezoelectric element according toclaim 2.